add: ui-switch style

add: virtual mode in Dropdown

lib/ui/css/dropdown.scss

@@ -152,21 +152,25 @@ $listMaxHeight: 210px;
     }
 
     >.ui-drop-list {
-        margin: 0;
-        padding: 0;
-        list-style: none;
         max-height: $listMaxHeight;
         overflow-y: auto;
+        position: relative;
         font-size: var(--font-size);
         @include scrollbar();
 
-        &.filtered>li:first-child {
+        &.filtered>.drop-content>.li:first-child {
             background-color: var(--hover-bg-color);
         }
 
-        >li {
+        >.drop-content {
+            position: absolute;
+            width: 100%;
+        }
+
+        li {
             // display: flex;
             // align-items: center;
+            list-style: none;
             line-height: $dropItemHeight;
             height: $dropItemHeight;
             padding: 0 10px;
@@ -186,4 +190,4 @@ $listMaxHeight: 210px;
             }
         }
     }
-}
+}